1. Field of the Invention
The present invention relates to a solar energy collecting device and, more particularly, an improved solar energy collecting device which is simple in structure, light in weight and less expensive to manufacture when compared with the conventional devices of the type incorporating a number of metal tubes.
2. Description of the Prior Art
In recent years, solar energy collecting devices have been used for various purposes other than merely preheating water for use in bathing. A prior art circulating type device has been constructed which comprises a number of tubular elements adapted to be exposed to solar rays while said tubes provide a through passage through which water is circulated by a pump to be supplied from a resevoir and returned to the same resevoir. This circulating type device is an improvement over a conventional prior art solar energy collecting device of the vessel type which is substantially a vessel adapted to contain a quantity of water which is directly exposed to the solar rays in said vessel. A solar energy collecting device of the conventional prior art circulating type generally comprises copper tubes, aluminium roll bond tubes or stainless tubes with or without encircling fins. However, these metal tubes are relatively heavy and expensive and not completely free from corrosion over a long period of service. Furthermore, since the metal tubes in the conventional solar energy collecting devices are generally assembled by soldering or welding, the manufacturing cost is relatively high. In addition, a stress concentration may be caused at various portions during the assembling procedure and further stress may result from a difference in thermal expansion in operation thereby sometimes causing cracking and subsequent leakage. In this conventional prior art structure, it is inconvenient to replace a tubular element damaged by corrosion or thermal cracking with a new one and such an exchanging process involves a considerable expense.